Refactor: Replace optimization level with boolean flag

The optimizer now uses a simple boolean flag (`optimization`) instead of
an `optimization_level` (u32). This simplifies the optimizer's logic and
makes it easier to enable or disable optimizations.

The command-line interface and internal testing have been updated to
reflect this change.

src/integration_test.rs

@@ -82,13 +82,13 @@ mod tests {
 
     #[test]
     fn test_examples() {
-        for level in 0..=2 {
-            let results = crate::utils::tester::run_functional_tests_with_level(level);
+        for opt in [false, true] {
+            let results = crate::utils::tester::run_functional_tests_with_optimization(opt);
             for res in results {
                 assert!(
                     res.success,
-                    "Example {} failed at level {}: {}",
-                    res.name, level, res.message
+                    "Example {} failed at opt {}: {}",
+                    res.name, opt, res.message
                 );
             }
         }
@@ -97,7 +97,7 @@ mod tests {
     #[test]
     fn test_debug_mode_logging() {
         let mut env = Environment::new();
-        env.optimization_level = 0;
+        env.optimization = false;
         let source = "(+ 10 20)";
         let result = env.run_debug(source).expect("Failed to run debug");